This application is based upon and claims priority of Japanese Patent Applications Nos. Hei 10-354305 and Hei 11-308827, filed, the contents being incorporated herein by reference.
a) Field of the Invention
The present invention relates to a magnetic material, magnetic head and magnetic storage device and particularly to a magnetic material, magnetic head and magnetic storage device having the characteristic for composition to improve high frequency characteristic of induction type head and MR head forming a composite type thin film magnetic head to be used in the magnetic storage device such as a Hard Disk Drive (HDD) or magnetic tape device.
b) Description of the Related Art
Because of growing of request in these years for reduction in size and expansion of capacity of a hard disk drive as an external storage device of computer, the recording frequency is reaching 100 MHz (108 Hz). In such magnetic storage device, the magnetic heads for writing and reading recording data are always integrally structured in such a manner that the write head for recording and the read head for reproducing are individually arranged. Namely, these heads are sequentially laminated as the layers in a series of filming process so that the recording head and reading heads are accurately arranged adjacently with less positional deviation in the narrow pitch for the write and read operation of magnetic recording medium in order to realize high density recording.
The upper magnetic pole layer of such a thin film magnetic head is often formed using a permalloy alloy such as Ni82Fe18 or the like which has been integrally formed by the mask plating method. Here, however, an example of the composite type thin film magnetic head of the related art will be explained with reference to FIG. 6.
FIG. 6 is a schematic perspective view of the essential portion of a composite type thin film magnetic head of the related art. A lower shield layer 41 consisting of NiFe alloy or the like is provided, through the Al2O3 film (not illustrated), on the Al2O3-TiC substrate (not illustrated) as the mother material of slider, a magnetic resistance effect element 42 consisting of a laminated structure, etc. of NiFe, Ti, NiFeCr is provided via a lower lead gap layer (not illustrated) such as Al2O3 or the like, these are then patterned in the predetermined shape and thereafter a read electrode 43 is formed by depositing a conductive film consisting of Au, etc. to both ends of the magnetic resistance effect element 42.
Next, a lower magnetic pole layer 44, which also works as the upper shield layer, consisting of NiFe alloy or the like is provided again via the upper lead gap layer (not illustrated) such as Al2O3 or the like and a write gap layer (not illustrated) consisting of Al2O3 or the like is provided thereon, a horizontal spiral type write coil 45 is formed via a lower inter-layer insulating film (not illustrated) such as resist, etc., a write electrode 46 is provided to both ends of such coil, and thereafter an upper magnetic pole layer 47 in such a shape as providing a narrow write pole 48 at the end part is provided via the upper interlayer insulating film (not illustrated) consisting of resist, etc.
Next, after the Al2O3 film is provided to the entire surface as a protection film (not illustrated), a substrate is cut, and machining and slider process including the grinding are performed for adjusting the length of write pole 48, namely the depth of gap. Thereby, a composite type thin film magnetic head in which the MR head for reproducing, namely for reading and an induction type thin film magnetic head for recording, namely for writing utilizing the magnetic resistance effect element 42 can be obtained.
In this case, a magnetic flux generated when a signal current flows into the write coil 44 from a write electrode 46 is guided to a magnetic pole core consisting of the lower magnetic pole layer 44 and upper magnetic pole layer 47, the magnetic flux leaks to the outside by the recording gap formed by the write gap layer at the area near the write pole 48 at the end part of the upper magnetic pole layer 47 and thereby signal is recorded to a recording medium. Moreover, on the contrary, the signal can also be reproduced by detecting the magnetic flux from the recording medium with the magnetic pole core, width of the write pole 48 at the end of the upper magnetic pole layer 47 becomes the track width and the surface recording density can be restricted by this track width.
On the other hand, the reproducing principle of the MR head utilizes the phenomenon that when a constant sense current flows from a read electrode 43, electrical resistance of magnetic thin film forming the magnetic resistance effect element 42 changes depending on the magnetic field from the recording medium.
However, there is a problem that the shield effect for magnetic field noise and drive magnetic field in the frequency of 10 MHz to several tens of MHz and magnetic recording capability in the magnetic shield and upper and lower magnetic pole layers in a composite type thin film magnetic head are largely lowered due to an eddy current loss and thereby recording defect may easily be generated. This problem may be generated because when the frequency becomes higher, an eddy current loss also increases and recording magnetic field intensity is lowered by the surface effect. In order to control such eddy current loss, it is enough that the specific resistance xcfx81 is raised because the eddy current loss is inversely proportional to the specific resistance xcfx81.
Namely, when a radius of magnetic thin film, namely thickness is xcfx84 [m], frequency is f [MHz], intensity of magnetization is Bm[Wb/m2] and specific resistance is xcfx81 [xcexa9xc2x7m], an eddy current loss We per unit volume flowing a magnetic material when a coil is wound around the column type magnetic material of radius 5[m] and a coil current is impressed thereto can be expressed as follow.
We=xcfx802xc2x7xcfx842xc2x7f2xc2x7Bm2/4xcfx81xe2x80x83xe2x80x83(1)
Therefore, when the specific resistance xcfx81 is large or when radius xcfx84 is small, an eddy current loss We becomes small.
Moreover, when specific resistance xcfx81, thickness of magnetic film is xcfx84, vacuum permeability is xcexco and permeability of magnetic film is xcexcd, the limit frequency fg is expressed as follow.
fg=4xcfx81/(xcfx80xc2x7xcexcoxc2x7xcexcdxc2x7t2)xe2x80x83xe2x80x83(2)
Therefore, when the specific resistance xcfx81 is large or thickness t is small, the limit frequency fg becomes large.
However, since the upper magnetic pole layer 47 and write pole 48 in the related art are themselves formed of permalloy such as Ni82Fe18 or the like, the specific resistance xcfx81 is as small as about 20 xcexcxcexa9cm and moreover since it is integrally formed of comparatively thick film by the plating, here rises a problem that values of xcfx84 or t become large, eddy current loss We unnecessarily becomes large and thereby the limit frequency fg unnecessarily becomes small.
On the other hand, when thickness t of magnetic film is set to a small value, eddy current loss We can be made small and the limit frequency fg can be made large. However, in this case, another problem that total magnetic flux becomes small is also generated.
In view of solving such problems, development is now being continued to attain the material having higher xcfx81 than that of permalloy such as Ni82Fe18 or the like. For example, it has been proposed to use, as the high frequency magnetic pole material, the NiFeMo alloy film having the magnetic characteristic almost identical to that of permalloy and specific resistance xcfx81 (xe2x89xa720 xcexcxcexa9cm) (if necessary, refer to Japanese Published Unexamined Patent Application No.: HEI 9-63016).
In the above, the NiFeMo alloy film proposed as the magnetic strain xcexs as large as exceeding 5xc3x9710xe2x88x926 and moreover requires the heat treatment in the temperature range of 180xc2x0 C. to 300xc2x0 C. for magnetic domain control. In this case, this heat treatment results in a problem that adverse effect will probably be applied on the magnetic resistance effect element forming the reproducing means formed before formation of the magnetic pole.
Namely, the magnetic stra1in xcexs must be small in order to obtain higher permeability of the magnetic pole layer of a thin film magnetic head (if necessary, refer to xe2x80x9cMagnetic Recording Engineeringxe2x80x9d by Matsumoto, et. al., p-179, Kyoritsu Publication) Moreover, the magnetic flux can be propagated through spin rotation in the hexagonal magnetic domain and reciprocal magnetization process having excellent high frequency response may be generated by conducting magnetic domain control to form the hexagonal magnetic domain up to the area near the end part of the magnetic pole, namely up to the area near the write pole.
Here, the upper magnetic pole layer of an ordinary shape of the related art is considered and ideal magnetic domain structure in the upper magnetic pole layer will be explained with reference to FIG. 7.
FIG. 7 is a plan view of the upper magnetic pole layer 47. As the ideal magnetic domain structure, it is expected that the hexagonal magnetic domain 50 which will become the main magnetic domain is formed up to the area near the write pole 48 and the magnetizing direction is circulated as indicated by the arrow mark through the triangular magnetic domain 51 which becomes the circulating magnetic domain formed adjacently to the hexagonal magnetic domain 50.
As explained above, there are three important factors of high specific resistance, small magnetic strain constant xcexs and magnetic domain control and moreover it is also essential to eliminate the process such as heat treatment which gives adverse effect to the magnetic resistance effect element or the like forming the reproducing means formed before formation of magnetic pole.
Accordingly, it is an object of the present invention to improve high frequency characteristic and to form excellent magnetic domain structure without introducing the heat treatment by controlling the composition ratio of NiFeMo in the magnetic material, magnetic head or magnetic storage device.
FIG. 1 is a diagram for explaining principle structure of the present invention and a means for solving the problem in the present invention will be explained with reference to FIG. 1.
FIG. 1 is a composition diagram indicating the preferable range of NiFeMo composition.
The present invention is characterized in that
(1) in a magnetic material consisting of Ni, Fe and Mo, the composition ratio of NiFeMo is selected under the condition where Ni is 77 to 82 atom %, Fe is 15 to 21 atom %, Mo is under 6 atom %, and magnetic strain constant xcexs is in the range of xe2x88x921xc3x9710xe2x88x926xe2x89xa6xcexsxe2x89xa60;
(2) In a magnetic material consisting of Ni, Fe and Mo, the composition ratio of NiFeMo is selected under the condition that Ni is 77 to 82 atom %, Fe is 15 to 21 atom %, Mo is under 6 atom % and magnetic strain constant xcexs is in the range of 0xe2x89xa6xcexsxe2x89xa61xc3x9710xe2x88x926.
In above items, the magnetic material selected under the condition of item (1) is preferable as the magnetic pole layer of an ordinary write head in the shape having compressed stress. Meanwhile, the magnetic material selected under the condition of item (2) is preferable as the magnetic pole material of write head in the shape having tensile stress.
A high permeability magnetic material having excellent high frequency characteristic can be obtained by controlling the composition ratio of NiFeMo to satisfy the above conditions and moreover when the upper magnetic pole layer is structured by a magnetic material film of such composition ratio, the magnetic domain structure identical to the ideal structure in which the hexagonal magnetic domain is formed up to the area near the end part of the upper magnetic pole layer can be obtained, for example, in regard to the magnetic material under the condition of item (1).
(3) Moreover, the present invention is also characterized in that the composition ratio of NiFeMo is selected so that the coercive force Hc of said magnetic material is in the range of Hcxe2x89xa61 Oe in the items (1), (2).
As explained above, excellent soft magnetic characteristic similar to that of permalloy required for magnetic pole layer can be obtained by selecting the composition ratio of NiFeMo so that the coercive force Hc of said magnetic material is in the range of Hcxe2x89xa61 Oe.
(4) Moreover, the present invention is also characterized in that the composition ratio of NiFeMo is selected so that a specific resistance xcfx81 is in the range of xcfx81xe2x89xa720 xcexcxcexa9cm in any one of the above items (1) to (3).
As explained above, the magnetic material having the specific resistance higher than that of permalloy such as Ni82Fe18 or the like of the related art can be obtained by selecting the composition ratio of NiFeMo so that the specific resistance xcfx81 is in the range of xcfx81xe2x89xa720 xcexcxcexa9cm. Thereby, eddy current loss We can be reduced and limit frequency fg can be raised.
(5) Moreover, the present invention is characterized in that the composition ratio of NiFeMo is selected so that the saturated magnetic flux density Bs of said magnetic material is in the range of Bsxe2x89xa70.8 T in any one of the above items (1) to (4).
As explained above, the saturated magnetic flux density almost identical to that of permalloy can be obtained by selecting the composition ratio of NiFeMo so that the saturated magnetic flux density Bs of said magnetic material is in the range of Bsxe2x89xa70.8 T Therefore, the recording magnetic field intensity similar to that of permalloy can be attained.
(6) Moreover, the present invention is characterized in that the magnetic pole layer of the magnetic head can be formed using any magnetic material of the items (1) to (5). As explained above, the magnetic domain structure almost identical to the ideal one can be obtained in the area near the end part of the upper magnetic pole layer, particularly the upper magnetic pole layer using any magnetic material of items (1) to (5) and thereby an induction type thin film magnetic head or a composite type thin film magnetic head having excellent high frequency characteristic can be realized.
(7) Moreover, the present invention is characterized in forming a magnetic shield layer of a magnetic head with any magnetic material of those of items (1) to (4).
As explained above, good shield effect for high frequency magnetic field noise and drive magnetic field can be maintained in the excellent condition by structuring the magnetic shield layers holding the magnetic resistance effect element using any magnetic material among those of items (1) to (4). Thereby, the MR head for reproducing and a composite type thin film magnetic head having excellent high frequency characteristic can be realized.
(8) Moreover, the present invention is characterized by forming the magnetic shield layer using any magnetic material among those of items (1) to (4) in the magnetic apparatus.
As explained above, application of magnetic shield layer is never limited to the magnetic head and, for example, in the magnetism measuring apparatus, such magnetic shield layer can also be used as the magnetic shield layer for shielding the external magnetic field as the source of noise.
According to the present invention, since the composition ratio of the NiFeMo alloy is selected to the value which assures excellent high frequency characteristic and provides the magnetic strain constant xcexs assuring easy formation of excellent magnetic domain structure without requiring the heat treatment, value of specific resistance xcfx81 can be enlarged without sacrifice of the other characteristics. Thereby, the high frequency characteristic can be improved to a large extent in view of improving the magnetic recording capability. As a result, the present invention can much contribute to high frequency.